Development and coating of new zinc oxide photoconducting recording systems



United States Patent 3,396,016 DEVELOPMENT AND COATING OF NEW ZINC OXIDEPHOTOCONDUCTING RE- CORDING SYSTEMS James R. Olson, Rochester, N.Y.,assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of NewJersey No Drawing. Filed Aug. 4, 1965, Ser. No. 477,307 12 Claims. (Cl.96-1.8)

This invention relates to electrophotography, particularly to novelphotoconductive insulating layers and electrophotographic platescomprising such layers and their use in electrophotography.

Electrophotographic plates comprising various particulatephotoconductors dispersed in electrically insulating binders weredescribed by Middleton in US. Patents No. 2,663,636 patented Dec. 22,1953 and No. 3,121,006 patented Feb. 11, 1964. Plates comprisingphotoconductive layers of zinc oxide dispersed in electricallyinsulating resin binders were described by Young and Greig in RCAReview, December 1954, .pp. 469-484 and in US. Patents No. 3,052,539 and3,052,540, both patented Sept. 4, 1962. Photoconductive insulatinglayers comprising a particulate photoconductor, as described in theprior art generally comprise, as an insulating binder for thephotoconductor, an electrically insulating synthetic polymeric resinsuch as silicone resins, metha-crylate resins, various polyester resins,polystyrenes, and the like. While some nonpolymeric compounds have beensuggested as binders for this use, generally the photoconductiveinsulating layers produced with binders of nonpolymeric materials havebeen less satisfactory for one or several of various reasons such aspoor electrical insulating quality, poor adhesion, reduced photographicspeed, incompatibility with photosensitizing dyes, discoloration, andthe like.

An object of the present invention is to provide photoconductiveelements for use in electrophotography having a novel photoconductiveinsulating layer comprising a particulate photoconductor such as zincoxide in a nonpolymeric binder. Another object is to providephotoconductive elements for use in electrophotography having especiallyfavorable electrical and photographic properties. Electrophotographicelements in accordance with the present invention, in specificembodiments, will have one or more of the advantages of favorablephotographic speed, favorable electrical dark resistivity, favorabledark decay properties, relatively favorable economy of manufacture, andfavorable surface appearance.

The present invention provides electrophotographic elements having aphotoconductive insulating layer which comprises a particulatephotoconductor such as zinc oxide dispersed in a nonpolymeric vehicleselected from sucrose esters, bisphenols, and mixtures of members ofthose respective classes of compounds with each other and with certainother nonpolymeric materials. In addition to a particulatephotoconductor and the binder, the photoconductive layers prefer-ablywill contain sensitizing amounts of photographic sensitizing dyes toincrease the photographic speed and to broaden the spectral sensitivityof the photoconductor. A particular advantage of certain photoconductivelayers made with nonpolymeric binders of the present invention is that avariety of eflective photosensitizing dyes can be used compatibly in thephotoconductive layer without adverse effect upon their sensitizingfunction by the binder materials. Another advantage of certain preferredelectrophotographic elements in accordance with the present invention isthat the photoconductive insulating surface retains its electricalresistivity at high relative humidities. Electrophotographic prints madeon preferred elements in accordance with the present invention comparefavorably in quality with photoconductive zinc oxide elements presentlyavailable commercially for use in electrophotography.

A first class of compounds which may be used as 'binders in accordancewith the present invention is the class of organic compounds calledbisphenols. This class of compounds can be characterized by thefollowing formula:

wherein X represents a single bond, a single atom, or a bivalent organicradical, and R and R may represent hydrogen or radicals substituted forhydrogen at any of the carbon atoms on the respective rings. X mayrepresent a bivalent organic radical having an ylidene carbon atom.Specific examples of bisphenols useful within the scope of the inventioninclude:

4,4-sulfamyl diphenol 1,3-(4-hydroxyphenol) propane p,p'-biphenol3,3-dipropy1-(p,p-diphenol) 4,4'-oxydiphenol diresorcyl sulfide4,4-sulfonyl diphenol 2,2'-dihydroxy benzophenone2,2-4,4-tetrahydroxybenzophenone 2,2-dihydroxy-4-methoxybenzophenone2,2-dihydroxy-4,4-dimethoxy benzophenone2,2-dihydroxy-4-n-octyloxybenzophenone4,4-dihydroxy-3,3'-dinitrobenzophenone 1,3-'(4-hydroxyphenyl)propane2,2'( ethane diylidene d initrilo)diphenol a,a-(ethylene dinitrilodi-o-cresol bis (2-hydroxyphenyl methane bis (4-hydroxyphenyl)methanebis(2,6-di-t-butyl-4-hydroxyphenyl)methane 1 l-bis (4-hydroxyphenylethane 1, l-bis (4-hydroxyphenyl -2-methyl propane 1, l-bis(4-hydroxyphenyl -3 -methyl butane 1 ,'1-bis(4-'hydroxyphenyl) -n-butane2,2-bis(4-hydr-oxyphenyl)propane 2,2-bis( 4-hydroxyphenyl)butane 2,2-bis(4-hydroxyphenyl) -3-methyl butane 2,2-bis (4-hydroxyphenyl) pentane2,2-bis (4-hydroxyphenyl) -4-rnethyl pentane2,2-bis/(4-hydroxyphenyl)hexane 2,2-bis (4-hydroxyphenyl) nonane2,2-bis(3-t-butyl-4-hydroxyphenyl)propane 3,3bis(4-hydroxyphenyl)pentanebis 4-hydroxyphenyl phenyl methane bis (4-hydroxyphenyl) naphthylmethane bis(4-hydroxyphenyl)-4-methylphenyl methanebis(4-hydroxyphenyl)-2-hydroxymethylphenyl methane bis (4-hydroxyphenyl)-2-chlorophenyl methane bis(4-hydroxyphenyl) -2,4-dichlorophenyl methanebis (4-hydroxyphenyl -4-chlorophenyl methane bis (4-hydroxyphenyl-3,4-dichlorophenyl methane bis(4-hydroxyphenyl) -2-carboxyphenylmethane bis 3-methyl-4-hydroxyphenyl) phenyl methane bis(4-hydroxyphenyl) diphenyl methane 1,1-bis(4-hydroxyphenyl) -1-phenylethane 1, 1-bis(4-hydroxyphenyl) -1-(4-methylphenyl) ethane 1,l-bis(4-hydroxyphenyl)-l-naphthyl ethane1,l-bis(4-hydroxyphenyl)-1-(3-fluorophenyl) ethane1,1-bis(4-hydroxyphenyl) -1-(4-fiuorophenyl)ethane1,1-bis(4-hydroxyphenyl)-1-(3,4,5-trifiuorophenyl) ethane1,1-bis(4-hydroxyphenyl)-1-(3 -chlorophenyl)ethane seasons 3 1,1-bis(4-hydroxyphenyl)-1-(4-chlorophenyl)ethane 1,l-bis(4-hydroxyphenyl)-1-(3 ,4-dichlorophenyl) ethane 1,1-bis4-hydroxyphenyl l -(2,5-dichlorophenyl ethane l, l-bis 4-hydroxyphenyl-1 (4-bromophenyl ethane 1, l-bis 3-methyl-4-hydroxyphenyl -1-(4-chlorophenyl) ethane1,1-bis(3-methyl-4-hydroxyphenyl)-1-(3,4-dichlorophenyl) ethane1,1-bis(3 ,5 -dichloro-4-hydroxyphenyl 1- 3,4-dichlorophenyl ethane 1,1-bis(4-hydroxyphenyl)1-phenyl pentane and the like.

The class of bisphenols includes esters containing more than onebisphenol moiety, for example, the diester obtained by condensing twomoles of 4,4-bis(4-hydroxyphenyl)-pentanoic acid with the glycolC36H72(OH)2.

A preferred embodiment using a bisphenol singly as a binder for zincoxide photoconductive coatings is described in Example I.

EXAMPLE I One gram of 2,2-bis (4-hydroxyphenyl)pentane was dissolved in6.75 grams acetone and 3.5 grams of photoconductive zinc oxide (TypeXX78, New Jersey Zinc Co.) sensitized with 1.O mole Bromophenol blue and0.84 lO mole anhydro-3,3-di-;3-carboxyethyloxacarbocyanine hydroxide permole of zinc oxide was added to the solution. The mixture was milled bya steel roll inside a steel cylinder for minutes and then the mixturewas spread on a support with a scraper bar having a .0O4-inch slit. Thecoating was dried by evaporation in air overnight. A coherent coatingwas obtained which was flexible and the surface had good resistance tochalking by abrasion. The finished coated element was tested todetermine dark resistivity of the insulating layer as indicated byinitial charge potential (V dark decay as indicated by the chargepotential on the surface /2 minute after charging (V and photographicspeed as determined by a standardized charging, exposing, and developingprocedure. This sample showed the following test results: V 340 volts, V190 volts, speed, 204.

By the procedure described in Example I, sample electrophotographicelements were made using other bisphenols listed above as binders. Testresults varied among the various samples but all of the samplesexhibited properties of some utility in electrophotography.

A second class of compounds which may be used as binders in accordancewith the present invention is sucrose esters, for example, esters formedby condensation of sucrose with monocarboxylic organic acids. Examplesof sucrose esters are sucrose octa-acetate, sucrose benzoate, sucrosediacetate hexaisobutyrate, sucrose benzoate isobutyrate, and the like.

A preferred embodiment having a sucrose ester used singly as a binder isdescribed in Example II.

EXAMPLE u A sample electrophotographic element was made by the proceduredescribed in Example I but using one gram sucrose benzoate isobutyrateinstead of the bisphenol. The finished sample had a relatively softphotoconductive insulating layer. The sample was tested forelectrophotographic properties with the following results: V 415, V 330,speed, 104.

Samples were made as in Example II but using the other sucrose estersmentioned above, singly, as binders for the respective samples. All ofthe samples were tested and exhibited useful electrophotographicproperties.

Especially preferred binder compositions comprise a mixture ofnonpolymeric compounds comprising a mixture of a bisphenol with asucrose ester. We have found that as a binder for the photoconductivecoating, the mixture of a sucrose ester and a bisphenol produces afinished photoconductive insulating coating having electrical propertiessuperior to those made with either of the binder EXAMPLE III Twentygrams sucrose diacetate hexaisobutyrate and 20 grams1,1-bis(4-hydroxyphenyl)-l-(4-chlorophenyl) ethane were dissolved in 250grams acetone. This solution was mixed with 140 grams Florence GreenSeal 8 zinc oxide sensitized as in Example I. The mixture was ballmilledfor 21 hours, then coated by extrusion hopper on Riegel brandelectrically conductive paper, Type KR39XE. The coating was dried by airheated to about 62-68 C. Finished samples were dark adapted in air of 50percent relative humidity at 74 F. overnight before testing. The sampleswere tested as in Example I. Results: V 370 volts, V 275 volts, speed,250.

Two component binder mixtures consisting of a sucrose ester and abis-phenol were made using various sucrose esters and various bisphenolsin varied combinations. Electrophotographic elements were made usingthese binder mixtures. These elements were made by the method describedin Example III. The proportion of sucrose ester in the respective bindermixes was varied from as little as 25 percent by Weight to as much aspercent by weight with the remaining proportion of the binder mix beinga selected bisphenol. The weight ratio of zinc oxide to binder mix invarious coatings was varied from 3:1 to 4:1 in preferred embodiments andmay be varied from about 1:1 to about 6:1 in some embodiments. Usefulelectrophotographic elements were obtained in all cases and especiallygood results were obtained using sucrose octa-acetate as the sucroseester and using 4,4'-(2- norbornylidene)-bis(2,6-dichlorophenol) as thebisphenol component. However, it should be emphasized that all of thetwo component sucrose ester-bisphenol binder mixtures tested producedelements having electrophotographic utility.

Coatings were made using three and four component binder mixturescomprising a sucrose ester with two or three other components allselected from other sucrose esters, biphenols, and rosin. Best resultswere obtained using sucrose octa-acetate as one of the components with abisphenol as one of the other components. A preferred embodiment of athree component binder comprising sucrose octa-acetate, a bisphenol androsin is described in the following example.

EXAMPLE IV Thirty-two and one-half grams sucrose octa-acetate, 5 gramsrosin and 2.5 grams 1,1-bis(4-hydroxyphenyl)- 1-(4-chlorophenyl)ethanewere dissolved in 250 grams acetone. The solution was added to gramszinc oxide (Florence Green Seal 8), sensitized as in Example I. Themixture was ballmilled, coated, and dried and the electrophotographicelement was tested, all as described in Example III. Test results: V 450volts, V 380 volts, speed, 164.

A four component binder was used in the following example.

EXAMPLE V Thirty grams of sucrose octa-acetate with 2.5 grams rosin, 5grams sucrose diacetate hexaisobutyrate and 2.5 grams of4,4-(2-norbornylidene)bis(2,6-dichlorophenol) were dissolved in 250grams acetone and the solution was added to 140 grams zinc oxide(Florence Green Seal 8, New Jersey Zinc Co.), sensitized as in ExampleI. The

dispersion was ballmilled, coated, dried and tested as described inExample III. Test results were: V 440 volts, V 355 volts, speed, 104.

The foregoing examples describe particulate, sensitized zinc oxide as apreferred photoconductor but the present invention in its broaderaspects contemplates elements having other particulate photoconductorssimilarly dispersed in the novel binders. For example, we might useother particulate photoconductors of the kinds described in theaforementioned US. patents. The examples above describe use of certainpreferred spectra sensitizing dyes but this invention in its broaderaspects contemplates use of other suitable sensitizers in the novelphotoductive coatings. For example, a photoconductive insulating layerin accordance with the invention might incorporate other sensitizingcompounds of the various kinds described in the aforementioned patents.Similarly, our novel photoconductive insulating layers may be coated onany supports suitable for making electrophotographic elements, forexample, on supports 'of kinds described in the aforementioned patents.

In testing the plates for electrophotographic properties, we employedconventional corona discharge apparatus and methods for imposing auniform charge on the insulating surface, and employed standarddensitometry apparatus and methods for photographic exposure.Development was 'by cascade development with commercial n-typeelectroscopic developer.

A particular advantage with preferred embodiments of the invention isthe considerable reduction in weight of the element which can beobtained by making coatings of about 2.0 gm. per sq. ft. and which willstill have suitable electrophotographic properties. This coating isabout /3 lighter than many of the zinc oxide-resin coatings of prior artand the reduction in copy weight is appreciable.

The invention has been described in considerable detail with particularreference to preferred embodiments thereof, but it will be understoodthat variations and modifications can be effected within the spirit andscope of the invention as described hereinabove and as defined in theappended claims.

I claim:

1. An electroph-otographic element comprising a support and coatedthereon a photoconductive electrically insulating layer comprising aparticulate photoconductor dispersed in a non-polymeric binder, whichbinder comprises from 25 to 100% 'by weight of sucrose ester, theremainder of said binder being non-polymeric organic material.

2. An electrophotographic element comp-rising a support and coatedthereon a photoconductive electrically insulating layer comprising aparticulate ph'otoconductor dispersed in a non-polymeric binder, whichbinder consists essentially of a sue-rose ester.

3. An electrophotographic element comprising a support and coatedthereon a photoconductive electrically insulating layer com-prising aparticulate photoconductor dispersed in a non-polymeric binder, whichbinder consists essentially of a bisphenol.

4. An electrophotographic element comprising a support and coatedthereon a photoconductive electrically insulating layer comprising aparticulate photoconductor dispersed in a non-polymeric binder, whichbinder compriies a mixture of a sucrose ester and a bisphenol.

5. An electrophotographic element comprising a support and coatedthereon a photoconductive electrically insulating layer comprising aparticulate photoconductor dispersed in a non-polymeric binderconsisting of at least 25 percent by weight of sucrose octa-acetate, atleast five percent by weight of a bisphenol and the remainder ofnon-polymeric organic material.

6. An electrophotographic element comprising a support and coatedthereon a photoconductive electrically insulating layer comprising aparticulate photoconductor dispersed in a non-polymeric binder whichcomprises at least 25% by weight of sucrose octa-acetate.

7. An electrophotographic element comprising a support and coatedthereon a photoconductive electrically insulating layer comprising aparticulate photoconductor dispersed in a non-polymeric binderconsisting of at least 25 by weight of sucrose octa-acetate, at least 5%by weight of 4,4 ('2 norbornylidene)bis(2,6-dichlorophenol) and theremainder of rosin.

8. In an electrophotographic element comprising a support and coatedthereon a photoconductive electrically insulating layer which comprisesa particulate photoconductor dispersed in an insulating film-formingvehicle, the improvement wherein said insulating vehicle consistsessentially of at least 25% of a sucrose ester and the remainder of atleast one material selected from sucrose esters, bisphenols, and rosin.

9. An electrophotographic element comprising a support and coatedthereon a photoconductive electrically insulating layer comprising aparticulate photoconduc-tor dispersed in a non-polymeric bindercomprising at least 25 sucrose ester, the remainder of said binderconsisting essentially of at least one non-polymeric material selectedfrom the group consisting of sucrose esters, bisphenols, and rosin.

10. An electrophotographic element comprising a support and coatedthereon a photoconductive electrically insulating layer comprising aparticulate photoconductor dispersed in a non-polymeric bindercomprising at least 25% sucrose octa-acetate, the remainder of saidbinder consisting essentially of at least one material selected from thegroup consisting of sucrose esters, bisphenols, and rosin.

11. The electrophotographic element defined in claim 9, said particulatephotoconductor being photoconductive zinc oxide.

12. The electrophotographic element defined in claim 10, saidparticulate photoconductor being photoconductive zinc oxide.

No references cited.

NORMAN G. TORCHIN, Primary Examiner.

J. C. COOPER, Assistant Examiner.

9. AN ELECTROPHOTOGRAPHIC ELEMENT COMPRISING A SUPPORT AND COATEDTHEREON A PHOTOCONDUCTIVE ELECTRICALLY INSULATING LAYER COMPRISING APARTICULATE PHOTOCONDUCTOR DISPERSED IN A NON-POLYMERIC BINDERCOMPRISING AT LEAST 25% SUCROSE ESTER, THE REMAINDER OF SAID BINDERCONSISTING ESSENTIALLY OF AT LEAST ONE NON-POLYMERIC MATERIAL SELECTEDFROM THE GROUP CONSISTING OF SUCROSE ESTERS, BISPHENOLS, AND ROSIN.